Potential carbon emissions dominated by carbon dioxide from thawed permafrost soils

Increasing temperatures in northern high latitudes are causing permafrost to thaw¹, making large amounts of previously frozen organic matter vulnerable to microbial decomposition². Permafrost thaw also creates a fragmented landscape of drier and wetter soil conditions^{3, 4} that determine the amount and form (carbon dioxide (CO₂), or methane (CH₄)) of carbon (C) released to the atmosphere. The rate and form of C release control the magnitude of the permafrost C feedback, so their relative contribution with a warming climate remains unclear^{5, 6}. We quantified the effect of increasing temperature and changes from aerobic to anaerobic soil conditions using 25 soil incubation studies from the permafrost zone. Here we show, using two separate meta-analyses, that a 10 °C increase in incubation temperature increased C release by a factor of 2.0 (95% confidence interval (CI), 1.8 to 2.2). Under aerobic incubation conditions, soils released 3.4 (95% CI, 2.2 to 5.2) times more C than under anaerobic conditions. Even when accounting for the higher heat trapping capacity of CH₄, soils released 2.3 (95% CI, 1.5 to 3.4) times more C under aerobic conditions. These results imply that permafrost ecosystems thawing under aerobic conditions and releasing CO₂ will strengthen the permafrost C feedback more than waterlogged systems releasing CO₂ and CH₄ for a given amount of C.